Photographic product and process for forming a white image viewable against a dark background



July 28, 1953 E. H. LAND 2,647,055

PHo'roGRAPRIc PRODUCT AND PRocEss FoR FoRMING A WHITE IMAGE vIEwABLE AGAINST A'DARK BACKGROUND Filed Nov. 6, 1946 Developed Silver Image Receiving Lover FIG. 3

I Imagsz Carrying Layer Backing Layer -Black Image Carrying Layer "wf Black lNon-HaIaiion Layer Patented July 28, 1953A .PHOTOGRAPHIC PRODUCT AND PROCESS FOR FORMING A WHITE vHHAGrE lVIEW- ABLE AGAINST A DARK BACKGROUND Edwin H. Land, Cambridge, Mass.,'assignor to Polaroid Corporation, Cambridge, Mass., a. corporation of Delaware Application November 6, 1946, Serial No. '708,007

Claims.

This invention relates to photography and more particularly to improved photographic products and processes.

A particular object of this invention is to provide a process for obtaining a positive image from a latent negative image contained n an exposed photosensitive layer, by forming, on a layer other than said photosensitive layer, .said positive image in terms of variations of the highlights thereof.

Another object of the present invention is to provide a photographic process wherein a positive image is created from a latent negative image by the selective precipitation of imageforming components to create the highlights of said positive image, and said image can be viewed as a transparency or against a dark background which furnishes the shadows.

Another object of the present invention is to provide, in a process of the above type, an additional image-forming reaction whereby .imageforming components are created both in terms of highlights and in terms of shadows.

Another object of the invention is to provide a product, for use with a process of the above type, which contains a substance capable of selectively creating a White precipitate to form a positive image in terms of variations of the highlights thereof.

These and other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties, and the Yrelation of elements, which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, wherein:

Figure l is a schematic sectional view of a preferred embodiment of the present invention;

Fig. 2 is a fragmentary, sectional view of the embodiment of the invention shown in Fig. 1, during the processing of the film unit;

Fig. 3 is a schematic sectional view of lamodifled form of the present invention;

Fig. 4 is a schematic, diagrammatic another modification of the invention;

Fig. 5 is a schematic, diagrammatic View of another modification of the invention; and

view of Fig. 6 is a schematic, diagrammatic view of another modication of the invention.

In general, this invention relates to processes Aand products whereby a direct, positive image of a subject image may be obtained in terms of white, or light-colored, 'image-forming components corresponding to the highlights of a subject image. This image formation mayor may not be supplemented by the additional formation of image-forming components corresponding to the shadows of the subject image.

For applications showing related subject matter, attention is called -to my applications .Serial No. 662,000, filed April 13, 1946, for Photographic Silver Transfer Product and Process, `including a Lead Salt (now Patent No. 2,584,029); Serial No. 64,870, filed December 11, 1948, for Photographic Product Comprising a Rupturable Container Carrying a Photographic Processing Liquid (now Patent No. 2,543,181); and Serial No. 700,931, led October B, 1946, for Photographic Product Comprising a Plurality of Rupturable Containers, Each Carrying a Liquid for Processing .Said Product (now Patent No. 2,607,685).

A positive image may be formed in several ways. In one of these an image is formed in terms of shadows and in another it is formed in terms of highlights. This invention relates pri-marin 'to the latter method of image formation. In this case, positive image-forming components are created, in each portion of the positive image, in terms of highlights and in proportion to the highlights of the corresponding portion of the subject image, i. e., in accordance with thev amount of light emanating from lthat portion of the subject image. Since the -exposureof a `portion of a photosensitive layer, and its .developability is a direct function of the amount of light emanating from a corresponding portion of a subject image, and since a developer will develop such -a Aportion as a direct function of this amount of light, this characteristic is vhere utilized to control a Apositive imageforming reaction where the amount of imageforming component `created is a direct function of the amount of development. Thus for an intense highlight portion of the subject image a large amount of the positive image-forming component is created, for a .middle tone a lesser amount .of image-forming component is created,

and 'for a shadow substantially no image-forming component is created.

The .present invention accordingly relates to a photographic process which comprises developing. exposed ,portions of -an exposed layer of photosensitive material, :containing a latent negative image of a subject image, forming, at some stage in the process, another layer into a permeable assembly with said photosensitive layer, and creating on said other layer a positive image of said latent negative image by forming a white r light-colored precipitate on said other layer whose density varies as a direct function of the density of said developed latent image, i. e., in accordance with the highlights of the subject image.

A novel composite photographic film unit for use with such a process comprises a layer of such photosensitive material, a developer for said photosensitive material, and another layer operatively associated With said photosensitive layer and adapted to carry a positive image, said other layer containing a material capable of selectively creating positive image-forming components under the selective control of the reaction of said developer and said photosensitive material as a direct function of the amount of development by said developer.

In a preferred form of the present invention there is provided a composite photographic lm unit shown in Figs. 1 and 2, Fig. l being an exaggerated fragmentary sectional view and Fig. 2 being a similar view of the film unit of Fig. 1 during processing. This lm unit preferably comprises a photosensitive layer I2 and another layer I4. The other layer I4 may serve several functions. In a preferred example it acts as a backing layer to permit the spreading of a liquid composition in a layer parallel to the photosensitive layer I2 and it also performs the additional function of serving as a permanent carrier for the final positive image. In less preferred forms of the invention it serves only either one of these functions or merely acts to carry certain of the reactive ingredients. In almost all cases, however, it will have the additional function of forming, with the photosensitive layer, a unit only slowly permeable to oxygen and within which a photographicV reaction may take place with substantial freedom from the effects of aerial oxidation. For convenience this layer I4 is referred to as an image-carrying layer. Between this layer and the photosensitive layer there is preferably included a rupturable container or pod I8 having therein a liquid composition. The

liquid composition preferably comprises a developer capable of developing a latent negative image formed in said photosensitive layer by the exposure thereof to actinic light. It also preferably contains a film-forming material which has a dual function of creating a film (referred to as an image-receiving layer) which adheres preferably to the image-carrying layer I4. The filmforming material imparts a desired viscosity to the liquid composition, so as to aid in spreading the liquid in a layer of uniform predetermined thickness between the photosensitive layer I2 and the image-carrying layer I4. The liquid composition also contains other materials, such as sodium hydroxide, which selectively enter into a precipitation-forming reaction with materials contained on the surface of the image-carrying layer nearest the photosensitive layer.

In Fig. 1 there is also provided, for carrying the photosensitive layer I2, a base layer I0, of suitable cellulosic film base, such as cellulose acetate, cellulose nitrate, or cellulose acetate butyrate. This base layer is preferably transparent so that exposure of the photosensitive layer I2 may be made through this base layer. However, by suitably rearranging portions of the film unit,

the base layer can be made of paper or otherv opaque material suitable for carrying a photosensitive emulsion on its surface. The base can also be made opaque, if desired, by the addition of suitable dyes or pigments to the above-named substances. Such opacity will be preferable depending upon hoW the lrn is exposed within the camera. It may also be made of an impermeable substance such as glass. When the base layer is opaque, the photosensitive layer may be exposed by causing relative movement between it and the image-carrying layer.

The photosensitive layer I2 is preferably a noble metal halide of the type which is made developable by exposure to actinic light. Such a photosensitive layer is preferably a silver halide emulsion, such as a silver halide, a mixture of silver halides, or a mixed silver halide. The image-carrying layer I4 in a preferred embodiment of the invention comprises a sheet of unhardened gelatin having thereon a coating of lead acetate and zinc acetate. It may also comprise a layer of unhardened gelatin on hardened gelatin, regenerated cellulose, polyhydroxy alkanes such as polyvinyl alcohol, sodium alginate, certain of the cellulose ethers such as methyl cellulose, and their derivatives such as sodium carboxymethyl cellulose or hydroxyethyl cellulose, carbohydrates such as gums or starch, and mixtures of these materials where the latter are compatible. A backing layer I6 is also provided and can be any suitable black or dark-colored opaque layer, such as black paper or a black dyed plastic lm. The container I8 has therein a liquid composition which preferably comprises an aqueous solution of a developer, sodium hydroxide, sodium sulflte and a film-forming material such as sodium carboxymethyl cellulose. The container is preferably formed of a substance such as an oxygen and water-vapor impervious material, such, for example, as a sheet of wax impregnated metal coated paper or Wax coated metal foil, or a metal foil coated with a resin, such as polyvinyl butyral, which is inert to alkalies. In a preferred form of the invention, the image-carrying layer I4 is a sheet of unhardened gelatin which is prepared by soaking, for a time of two minutes, in a solution containing 250 cc. of a 45% water solution of lead acetate and 10 grams of zinc acetate.

A preferred liquid composition to be carried by the container for use with the above image-carrying layer comprises 2.7 grams of sodium sulfite, 3.9 grams of sodium hydroxide, 2.7 grams of hydroquinone, 5 grams of sodium carboxymethyl cellulose, and 96 cc. of water.

When the film unit of the type described above is used, the film unit is positioned in the camera and the photosensitive layer I2 is exposed to actinic light preferably through the base layer I0. The film unit is then processed by applying thereto a mechanical stress, such as by passing the lm unit through a pair of pressure rollers, the container endgoing first. The pressure rollers act to rupture the container and spread the liquid composition in a uniform thin layer between the photosensitive layer and the imagecarrying layer. This uniform thin layer of the liquid composition is shown in Fig. 2 at 20 and is designated, for convenience, as an image-receiving layer. This image-receiving layer 20 is preferably of such thinness that the unit area thereof contains just a suflicient quantity of developer so that a fully developable portion of the latent image will completely react with the deafcavgoue v'eloper" available for reaction therewith. This condition is preferably obtained by utilizing a highly concentrated liquid composition in a very thin layer. The thinness and high concentration of the layer is believed to be of considerable importance since it apparently enables this liquid layer to assume the properties of a discontinuous nlm. In other words, it apparently acts as a number of minute, separate solutions. When the developer reacts with the photosensitive material in layer l2, it apparently lowers the pH in that area in proportion to the amount of reaction. This pH appears to be lowered as a direct function of the amount of development and therefore as a direct function of the intensity of the highlights in the subject image. Thus, where the latent image is densest (i. e., where the most light has reached it), the development of the negative is the maximum and the pH is apparently the lowest, about 5 to 6. On the other hand, where no development of the negative occurs, the pH apparently is quite high, -about 8. It is believed that this change in pH permits the selective formation of a white precipitate on the image-carrying layer. This white precipitate, in any event, does form as a direct function of the density of the highlights. Thus, where there is a maximum exposure of photosensitive material in a certain portion of the photosensitive layer, there is a maximum creation of white precipitate on the corresponding portion of the image-carrying layer, and likewise, where there is no exposure of the photosensitive material, there is no formation of white precipitate on the corresponding portion of the image-carrying layer. This lowering of the pH apparently enables the other elements of the liquid composition to form with the lead acetate and/'or the zinc acetate, insoluble, white precipitates. It is not known exactly to what extent the various elements of the liquid composition form these white precipitates, nor is it known exactly why these white precipitates are formed.

It is believed that these lead and/or zinc ions form corresponding metal hydroxides by reaction with the hydroxyl ions in the liquid composition, the formation and/or precipitation of the relatively insoluble metal hydroxides being a function of the pH of the solution. They are formed, however, and apparently their formation depends upon the pH ofthe solution in which they are formed. In other words, they form readily and densely where the pH is low; whereas they will not form in those portions of the liquid layer where the pI-I is high.

It can be seen from Fig. 2 that a white precipitate has formed in the image-receiving layer and also partially on the surface of the image-carrying layer Iii, wherever development of the silver halide in the corresponding portion of the photosensitive layer has taken place. There is thus reproduced a positive image in terms of the highlights, the highlights being formed by the white precipitate.

The above-outlined process creates a positive image on the image-carrying layer lll which comprises a white precipitate and whose density varies in proportion to the amount of light reaching the photosensitive layer I2. In a preferred embodiment, the layer i4, carrying on its surface an image in terms of white precipitate, is separated from the photosensitive layer I2 and the base layer Ill. When the vwhite image is viewed against the black, opaque background furnished by layer i6, a positive image corre- 6 spending to thesubject image is seen, thehigiJ lights Abeing formed by the white precipitateand the shadows being formed by said opaque black background.

It has also been found possible to produce this white-precipitate by using merely lead acetate alone on the image-carrying layer I4. However, it has been found that the density of the white image obtained is considerably increased when the lead acetate and zinc acetate are used in combination. A mixture of aluminum acetate and lead acetate on the image-carrying layer also results in the selective formation of the white precipitate.

In another modification of the present invention, it is contemplated to form not only the positive image in terms of whites, but to form simultaneously therewith a positive image in terms of blacks.` In other words, two separate, distinct, image-forming reactions are carried out at the same time.v This modication of the invention may be practiced by adding to the liquid composition mentioned above 0.75 gram of sodium thiosulfate, the other elements of the combination remaining the same When this latter liquid composition is spread between the photosensitive layer and the image-carrying layer, the developer develops the exposed photosensitive material and apparently lowers the pI-I in those corresponding regions of the liquid layer. However, in those portions of the photosensitive layer which are not completely developed by the developer and corresponding to portions less fully exposed, the sodium thiosulfate forms soluble silver complexes with the unexposed silver halide and transfers these soluble silver complexes to the adjoining liquid layer which is being converted at the same time to a dimensionally stable film. Here, the silver complexes are reduced to colloidal particles comprising silver to form a black image. There is thus formed, simultaneously, a positive image in terms of whites, corresponding to the intensity of the highlights in the subject image, and in blacks, corresponding to the depth of the shadows in the subject image.

One advantage of this double image formation is that it obviates the necessity for using an additional opaque backing for the lnal positive image,l since the image is formed completely, both in terms of blacks and whites. This modification of the invention is shown in Fig. S, where like numbers correspond to like elements of Figs. 1 and 2. As shown in Fig. 3, the invention ccntemplates using a silver halide solvent such as sodium thiosulfate in the liquid composition, thereby forming a black image as well as a white image, which allows the use of a transparent image-carrying layer 24.' This permits the exposure of photosensitive layer I 2 through layer 2li. When the positive image is formed between the adjacent surfaces of the photosensitive layer I2 and the image-carrying layer 24, it can be viewed through the image-carrying layer 24 and no layers need beseparated after processing of the lm.- 'l It may be desirable, in some cases, to separate the image-carrying layer 24 from the photosensitive layer assembly comprising layers I0 and I2. Thisis due to the fact that the image will appear geometrically reversed when looked at from the side of layer 24 which was closest to the photosensitive layer unless a special optical system is employed. It is quite possible, however, to leave the layer 24 in contact with the photosensitive layer after processing, and during the life of the finished positive` image,` particularly where exposure of the photosensitive layer is through the base layer IU.

It is also possible to create a black background for this white image, during the course of processing the photographic film unit by providing a separate container within the lfilm unit, adapted to contain a black dye. Such a modification of the invention is shown in Fig. 4 Where like numbers correspond to like elements of Figs. 1, 2, and 3. In this modification of the invention there is provided, in addition to the elements of the combination shown in Fig. 3, a separate liquid container 30, having therein, in a preferred form, a black dye incorporated in a water-soluble nlm-forming material such as polyvinyl alcohol. There is also provided a backing layer 26.

In the use of the modification of the invention shown in Fig. 4 the exposure of the photosensitive layer I2 is through the image-carrying layer 24 and transparent backing layer 26. After exposure, the film is processed by applying a mechanical stress thereto, such as by running the film unit through a pair of pressure rollers, the container end going first. This stress releases the two liquids from the two containers and spreads them in uniform parallel layers. The liquid composition from container I8 develops the latent negative image in the photosensitive layer and f produces a positive image in terms of White precipitate on the gelatin image-carrying layer 24. The liquid composition from the container 30 forms a black, opaque layer between the imagecarrying layer 24 and the backing layer 26 and forms a black background for the positive image which is rendered in terms of whites.

It is equally possible, of course, and in some cases, it may be desirable, to expose the photosensitive layer through the image-carrying layer, subsequently to separate the image-carrying layer, and to have the transparent image-carrying layer converted to a uniform black. This can be practiced in a number of ways, such as by including in the image-carrying layer a dyeforming material which is capable of reacting with a dye-forming component of the liquid composition, to form therewith an immobile black dye. Thus, when the liquid composition is spread in contact with the image-carrying layer, it is converted to a black, opaque layer.

It is also possible to form, in addition to the white precipitate image, a black or colored image, by the use of the unreacted developer technique disclosed in my copending application, Serial No. 702,039, filed October 8, 1946, for Photographic Product and Process. In this case, in addition to the materials such as lead acetate and zinc acetate, with which the image-carrying layer is coated, there is also provided a material capable of creating a color by formation of a pigment or a dye. Such a material can be a reducible metallic salt which is capable of reacting with unoxidized portions of the developer to form, as a result of this reaction, colloidal image-forming components. Such a material may also be a dye former capable of coupling to selectively form an immobile dye image corresponding to the shadows. It is also possible to use a developer, which, when oxidized byaerial oxidation or by an oxidizing agent contained on the imagecarrying layer, couples with itself or with a dye former contained in the image-carrying layer to form a black or other deep color. This selective image formation is possible, due to the fact that the 'amount of developer is so adjusted that, in the portions of the image corresponding to the highlights, the developer is completely reacted and trapped in the photosensitive layer by reaction with the exposed photosensitive material. Where the developer is unreacted it forms a positive image corresponding to the shadows of the subject image.

In the modification of the invention described in connection with Fig. l, there was provided a vtransparent image-carrying layer I4 which had an opaque black backing layer I6, against which the white image could be viewed. It is equally possible to combine the function of these two layers in one layer and to have a single imagecarrying layer which is black and opaque. Such a modification of the invention is shown in Fig. 5 where like numbers correspond to like elements of Fig. 1. In this modification of the invention there is provided the usual base layer Il) carrying on its inner surface the photosensitive layer I2. There is next provided a container I8, adapted to have therein a liquid composition comprising a developer, a film-forming composition, and the other materials ordinarily utilized in the embodiment of the invention shown in Fig. 1. There is also provided an image-carrying layer 45, which in a preferred form, is made of a sheet of black opaque paper. The image-carrying layer 44 preferably has incorporated, on its upper surface, lead acetate and zinc acetate which are designed to aid in the formation of a White precipitate.

In the use of the invention shown in Fig. 5, the photosensitive layer is exposed to actinic light, either through the base layer I0, or the base layer IIJ, carrying the photosensitive layer I2, is moved relative to the image-carrying layer 44 .so as to permit exposure of the inner surface of the photosensitive layer. After exposure of the photosensitive layer to actinic light, the film unit is processed in the usual manner by passing the film unit through a pair of pressure rollers, thus releasing the liquid from the container I8 and spreading it in a uniform thin layer between layers I2 and 44. When the liquid layer exists between layers I2 and 44, it develops the latent image produced in the photosensitive layer by exposure thereof, and also produces a white precipitate image on the surface of the image-carrying layer 44 and Within the imagereceiving layer which is formed by the film-forming material contained in the container I 8, as discussed in connection with Fig. 1 and the other figures. There is thus produced a positive image of the latent image in terms of white corresponding to the highlights thereof. The image-carrying layer 44, having on its surface the imagereceiving layer, which contains the white precipitate image, is preferably separated from the photosensitive layer so that the final positive image can be viewed. The positive image is a white precipitate with the black opaque imagecarrying layer 44 serving as a background.

In Fig-3 there was shown a modification of the invention which permits viewing of the final positive image Without separating any of the elements of the film unit. Another modification of the invention which serves the same function is shown in Fig. 6. This modification of the invention utilizes an opaque nonhalation layer as the background. In Fig. 6 like numbers correspond to like elements of Fig. 3. There is provided the usual base layer I0, having on its inner surface the photosensitive layer I2. On the inner surface of thev photosensitive layer l2v there is provided a black, opaque, water-permeable, nonhalation layer 3d. This layer Se is preferably formed of a suspension of lamp black in gelatin. There is next provided aA liquid container i8 adapted to have therein a liquid composition comprising a developer, a film-forming material, an alkali, and water. There is also provided a transparent image-carrying layer 243. In one modification of the invention the image-carrying layer 24 comprises a layer of transparent gelatin having on its upper surfaceA a lead acetate or other lead salt, plus zinc acetate. Where the adhesion of the hlm-forming material to the image-carrying layer 2d is particularly desired, this lead salt may preferably be used in the form of a lead salt of a linear high polymer such as lead carboni/methyl cellulose. In this case, excellent adhesion is obtained between the lead polymer salt and the polymeric hlm-forming material in the liquid composition, particularly where the nim-forming material is a similar polymer, such as sodium carbogymethyl cellulose.

In another modiiication o1 the invention, the image-carrying layer 2li is additionally coated with a soap solution which prevents the adhesion of the nlm-forming material, from container lil, to the image-cari lng layer 2d. In this modification, the imageecarrying layer actually serves as a backing layer, it can be stripped from the image-receiving layer formed by the nlm-forming material.

In the use of the modilication of the invention.

shown in Fig. 5, the photosensitive layer i2 is exposed to actinic .light through the base layer lil. The film unit is then processed in the usual manner, such as by passing through a pair of pressure rollers, thus releasing the liquid composition from the container i8 and spreading it in a uniform thin layer between the imagencarrying layer Zi! and the nonhalation layer Srl. The usual imageforming. reaction, as discussed in connection with Fig. 3, thereupon takes place, the latent image in the photosensitive layer is developed, and a white precipitate is formed in the imagereceiving layer due (it is believed) to the varying pH created by the developin Y reaction. In this stage or the process, it is apparent that there exists in the image-receiving layer, formed by the film-form ing material, a white precipitate image corresponding to the highlights of the positive image.

This image may be viewed through the transparent image-carrying layer 265 and it is not necessary to separate any of the elements of the combination. The transparent image-carrying layer acts as a protective surface for the final positive image. Ii, for any reason, it is desired to separate the :cage-carrying layer 2li from the iinal positive image, this can be accomplished more easily if the image-carrying layer has been previously coated with the soap solution to give a nonadhering surface with respect to the imagereoeiving layer.

In the above discussion of Fig. 6 it can be. seen that the nonhalation layer 3e' serves two functions. In the i'lrst place, it serves as a nonhalation layer for the exposure of the photosensitive layer l2. Secondly, it serves as a backing for the positive image produced in terms of whites in the image-receiving layer, It is also possible to give to this layer an additional function of supplying several of the reactive materials to the liquid cornposition. in this modification of the invention, it is possible to include, within this nonhalation layer Sd, the reactive materials such as lead salts or zinc salts. These salts may also be in the form l@ of a; citrate or a tartrate. This particular modiiicationof the invention is of advantage when a very smooth-surfaced image-carrying layer is utilized such as cellophane, that is, one which does not readily carry Ion its surface the reactive salts.

It is also contemplated by the present invention to include certain ofthe materials, ordinarily carried by the liquid, in solid form within the nlm unit.` In this case the. liquid composition may comprise only a solvent, i. e., Water, or an aqueous alkaline solution of a film-forming material. Such modications. of the invention are within the scope. of the above description.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description ory shown in the accompanying drawing shall be interpreted as illustrative and vnot in a limiting sense.

What is claimed is:

1. A photographic product comprising a plurality of layers including at least a photosensitive silver halide layer, a base layer for receiving a reverse image of a latent image in said photosensitive layer, and a, container holding at least an alkaline liquid solvent composition for a photographic developer, said photosensitive layer, said base layer and said container being so arranged as to permit at least a portion of said base layer and said photosensitive layer to 'be superposed with said container positioned for release of its liquid content between two layers of said product for permeation of said photosensitive and said base layers upon rupture of the container, said product having positioned therein a silver halide developer, said developer being soluble in said composition and being rendered effective upon release of said composition to develop a latent negative image in said photosensitive layer of a Subj ect to which said photosensitive layer has been exposed and, as a result of said development, causing an imagewise variation in the alkalinity of said liquid composition whereby the alkalinity of the composition adjacent areas of developed silver is lowered, said product, in addition, including in said base layer for said reverse image a substantially uniform distribution of a material comprisingV at least one metallic salt which is soluble in said liquid composition and which has a metallic ion reactable with the hydroxyl ion of said liquid composition to form a whitish precipitate when the alkalinity of said liquid composition has been lowered as a result of development whereby to provide a reverse image of said developed latent image in terms of the. highlights yof said subject, said developer being in a quantity sufcient to develop said latent image and said liquid composition. being in a quantity sufficient to dissolve all of said developer and' to react, in places where silver developmenthas occurred, with said metallic salt to provide said reverse image, and said productinoluding an opaque, black, water-permeable layer carried4 by said photosensitive layer on the side thereof adapted to be positioned in facing relation to said base layer when the photosensitive layer and the base layer are superposed, and wherein saidbase layer is transparent and said black layer provides nonhalation means and', in addition thereto, a. black background against which said reversehnage formerly-off white precipitate is readily viewable4 2. A, 1,Jhotographic prod-uct comprising a plurality of layers including4 at least. a photosensitive silver halide layer, a base layer for receiving a reverse image of a latent image in said photosensitive layer, and a container holding at least an alkaline liquid solvent composition for a photographic developer, said photosensitive layer, said base layer and said container being so arranged as to permit at least a portion of said base layer and said photosensitive layer to be superposed with said container positioned for release of its liquid content between two layers of said product for permeation of said photosensitive and said base layers upon rupture of the container, said product having positioned therein a silver halide developer, said developer being soluble in said composition and being rendered effective upon release of said composition to develop a latent negative image in said photosensitive layer of a subject to which said photosensitive layer has been exposed and, as a result of said development, causing an imagewise variation in the alkalinity of said liquid composition whereby the alkalinity of the composition adjacent areas of developed silver is lowered, said product, in addition, including in said base layer for said reverse image a substantially uniform distribution of a material comprising at least one metallic salt which is soluble in said liquid composition and which has a metallic ion reactable with the hydroxyl ion of said liquid composition to form a whitish precipitate when the alkalinity of said liquid composition has been lowered as a result of development whereby to provide a reverse image of said developed latent image in terms of the highlights of said subject, said developer being in a quantity suilicient to develop said latent image and said liquid composition being in a quantity sufficient to dissolve all of said developer and to react. in places where silver development has occurred, with said metallic salt to provide said reverse image, and said product, in addition to said photosensitive layer and said base layer, also including a black and substantially opaque layer which is located in said product adjacent one side of said base layer and which is adapted to provide a black background against which the image-forming white precipitate is readily viewable.

3. A photographic product comprising a plurality of layers including at least a photosensitive silver halide layer, a base layer for receiving a reverse-image of a latent image in said photosensitive layer, and a container holding at least an alkaline liquid solvent composition for a photographic developer, said photosensitive layer, said base layer and said container being so arranged as to permit at least a portion of said base layer and said photosensitive layer to be superposed with said container positioned for release of its liquid content between two layers of said product for permeation of said photosensitive and said base layers upon rupture of the container, said product having positioned therein a silver halide developer, said developer being soluble in said composition and being rendered effective upon release of said composition to develop a latent negative image in said photosensitive layer of a subject t which said photosensitive layer has been exposed and, as a result of said development, causing an imagewise variation in the alkalinity of said liquid composition whereby the alkalinity of the composition adjacent areas of developed silver is lowered, said product, in addition, including in said base layer for said reverse image a substantially uniform distribution of a material comprising at least one metallic 5211i',

which is soluble in said liquid composition and which has a metallic ion reactable with the hydroxyl ion of said liquid composition to form a Whitish precipitate when the alkalinity of said liquid composition has been lowered as a result of development whereby to provide a reverse image o'f said developed latent image in terms of the highlights of said subject, said developer being in a quantity suiiicient to develop said latent image and said liquid composition being in a quantity sufcient to dissolve all of said developer and to react, in places where silver development has occurred, with said metallic salt to provide said reverse image, and said product also comprising a second container holding a liquid having coloring matter included therein, said second container being positioned for releasing its liquid for distribution over one layer of the product and said liquid when released and distributed over the last-mentioned layer at least providing a substantially black and opaque stratum there- 4. A photographic product as defined in claim 3 wherein said liquid in said second container is a viscous organic film-forming material capable of providing on the layer over which it is distributed a thin lm which contains said coloring matter.

5. A photographic product as defined in claim 3 wherein said liquid in said second container is capable of penetrating into the layer over which it is spread and of carrying said coloring matter into said layer.

6. A photographic product comprising a plurality of layers including at least a photosensitive silver halide layer, a base layer for receiving a reverse image of a latent image in said photosensitive layer, and a container holding at least an alkaline liquid solvent composition for a photographic developer, said photosensitive layer, said base layer and said container being so arranged as to permit at least a portion of said base layer and said photosensitive layer to be superposed with said container positioned for release of its liquid content between two layers of said product for permeation of said photosensitive and said base layers upon rupture of the container, said product having positioned therein a silver halide developer, said developer being soluble in said composition and being rendered effective upon release of said composition to develop a latent negative image in said photosensitive layer of a subject to which said photosensitive layer has been exposed and, as a result of said development, causing an imagewise variation in the alkalinity of said liquid composition whereby the alkalinity of the composition adjacent areas of developed silver is lowered, said product, in addition, including in said base layer for said reverse image a substantially uniform distribution of a material comprising at least one metallic salt which is soluble in said liquid composition and which has a metallic ion reactable with the hydroxyl ion of said liquid composition to form a whitish precipitate when the alkalinity of said liquid composition has been lowered as a result of development whereby to provide a reverse image of said developed latent image in terms of the highlights of said subject, said developer being in a qua-ntity sufficient to develop said latent image and said liquid composition being in a quantity suflicient to dissolve all of said developer and to react, in places where silver development has occurred, with said metallic salt to provide said reverse image, and said product including a darkcolored and substantially opaque layer which is adapted to provide a dark background against which the image-forming white precipitate is readily viewable.

7. The process of forming a positive image in terms of the highlights of a subject which is to be photographed and recorded, said process comprising permeating an alkaline solution of a silver halide developer into a silver halide photosensitive layer containing a negative latent image of l said subject and also into a base layel` which is arranged in superposed relation to said photosensitive layer and which has incorporated therein a substantially uniform distribution of a material comprising at least one metallic salt of the character soluble in said solution and having a metallic ion reactable with the hydroxyl ion of said solution when the alkalinity of said solution is lowered below its initial alkalinity, whereby to provide a whitish precipitate, maintaining said photosensitive layer and said base layer in said superposed relation and developing said latent image to silver, with developer permeated into said photosensitive layer, while forming as a result of silver development an imagewise variation in the alkalinity of said solution whereby the alkalinity of said solution adjacent areas of developed silver is sufficiently lowered so that portions of said lowered alkalinity of said solution react with said metallic salt to provide said whitish precipitate, and depositing said whitish precipitate on a substantially black and opaque stratum of material at least carried by one of said layers.

8. The process as defined in claim 7 wherein said base layer comprises a substantially black and opaque material and provides said stratum.

9. The process as defined in claim 7 including the step of forming said substantially black and opaque stratum while permeating said solution and developing said latent image.

10. The process of forming a positive image in terms of the highlights of a subject which is to be photographed and recorded, said process comprising permeating an alkaline solution of a silver halide developer into a silver halide photosensitive layer containing a negative latent image of said subject and also into a base layer which is arranged in superposed relation to said photosensitive layer and which has incorporated therein a substantially uniform distribution of at least one material selected from the class of metallic salts consisting of lead, zinc and aluminum salts having a metallic ion reactable with a hydroxyl ion of said solution when the alkalinity of said solution is lowered below its initial alkalinity, whereby to provide a whitish precipitate, maintaining said photosensitive layer and said base layer in said superposed relation and developing said latent image to silver, with developer permeated into said photosensitive layer, while forming as a result of silver development an imagewise variation in the alkalinity of said solution whereby the alkalinity of said solution adjacent areas of developed silver is sufficiently lowered so that portions of said lowered alkalinity of said solution react with said metallic salt to provide said whitish precipitate, and depositing said whitish precipitate on a substantially black and opaque stratum of material at least carried by one of said layers.

11. The process as defined in claim 10 wherein said material reactable with the hydroxyl ion is a lead salt.

12. The process as defined in claim 10 wherein said material reactable with the hydroxyl ion is a mixture of a lead salt and a zinc salt.

13. The process as defined in claim 10 wherein said material reactable with the hydroxyl ion is a mixture of a lead salt and an aluminum salt.

14. The process as deiined in claim 10 wherein said material reactable with the hydroxyl ion is a mixture of lead acetate and zinc acetate.

15. The process of forming a positive image in terms of the highlights of a subject which is to be photographed and recorded, said process comprising permeating an alkaline solution of a silver halide developer into a silver halide photosensitive layer containing a negative latent image of said subject and also into a base layer which is arranged in superposed relation to said photosensitive layer and which has incorporated therein a substantially uniform distribution of a material comprising at least one metallic salt of the character soluble in said solution and having a metallic ion reactable with the hydroxyl ion of said solution when the alkalinity of said solution is lowered below its initial alkalinity, whereby to provide a whitish precipitate, maintaining said photosensitive layer and said base layer in said superposed relation and developing said latent image to silver, with developer permeated into said photosensitive layer, while forming as a result of silver development an imagewise variation in the alkalinity of said solution whereby the alkalinity of said solution adjacent areas of developed silver is sufiiciently lowered so that portions of said lowered alkalinity of said solution react with said metallic salt to provide said whitish precipitate, and depositing said whitish precipitate von a dark-colored and substantially opaque stratum of the material at least carried by one of said layers.

EDWIN H. LAND.

References Cited in the i'lle of this patent UNITED STATES PATENTS Number Name Date 2,013,159 Lierg Sept. 5, 1935 2,315,966 Knott Apr. 6, 1943 2,322,005 Fierke et al June l5, 1943 2,322,006 Fierke et al. June 15, 1943 2,322,027 Jelley et al June 15, 1943 2,322,037 Lindquist June 15, 1943 2,336,299 Russell Dec. 7, 1943 2,352,014 Rott June 20, 1944 2,366,723 Galley Jan. 9, 1945 2,388,894 Yackel Nov. 13, 1945 2,397,015 Kendall Mar. 19, 1946 2,410,644 Fierke Nov. 5, 1946 2,417,713 Stein Mar. 18, 1947 2,500,421 Land Mar. 14, 1950 2,584,029 Land Jan. 29', 1952 FOREIGN PATENTS Number Country Date 392,424 Great Britain May 18, 1933 879,995 France Mar. 10, 1943 

1. A PHOTOGRAPHIC PRODUCT COMPRISING A PLURALITY OF LAYERS INCLUDING AT LEAST A PHOTOSENSITIVE SILVER HALIDE LAYER, A BASE LAYER FOR RECEIVING A REVERSE IMAGE OF A LATENT IMAGE IN SAID PHOTOSENSITIVE LAYER, AND A CONTAINER HOLDING AT LEAST AN ALKALINE LIQUID SOLVENT COMPOSITION FOR A PHOTOGRAPHIC DEVELOPER, SAID PHOTOSENSITIVE LAYER, SAID BASE LAYER AND SAID CONTAINER BEING SO ARRANGED AS TO PERMIT AT LEAST A PORTION OF SAID BASE LAYER AND SAID PHOTOSENSITIVE LAYER TO BE SUPERPOSED WITH SAID CONTAINER POSITIONED FOR RELEASE OF ITS LIQUID CONTENT BETWEEN TWO LAYERS OF SAID PRODUCT FOR PERMEATION OF SAID PHOTOSENSITIVE AND SAID BASE LAYERS UPON RUPTURE OF THE CONTAINER, SAID PRODUCT HAVING POSITIONED THEREIN A SILVER HALIDE DEVELOPER, SAID DEVELOPER BEING SOLUBLE IN SAID COMPOSITION AND BEING RENDERED EFFECTIVE UPON RELEASE OF SAID COMPOSITION TO DEVELOP A LATENT NEGATIVE IMAGE IN SAID PHOTOSENSITIVE LAYER OF A SUBJECT TO WHICH SAID PHOTOSENSITIVE LAYER HAS BEEN EXPOSED AND, AS A RESULT OF SAID DEVELOPMENT, CAUSING AN IMAGEWISE VARIATION IN THE ALKALINITY OF SAID LIQUID COMPOSITION WHEREBY THE ALKALINITY OF THE COMPOSITION ADJACENT AREAS OF DEVELOPED SILVER IS LOWERED, SAID PRODUCT, IN ADDITION, INCLUDING IN SAID BASE LAYER FOR SAID REVERSE IMAGE A SUBSTANTIALLY UNIFORM DISTRIBUTION OF A MATERIAL COMPRISING AT LEAST ONE METALLIC SALT WHICH IS SOLUBLE IN SAID LIQUID COMPOSITION AND WHICH HAS A METALLIC ION REACTABLE WITH THE HYDROXYL ION OF SAID LIQUID COMPOSITION TO FORM A WHITISH PRECIPITATE WHEN THE ALKALINITY OF SAID LIQUID COMPOSITION HAS BEEN LOWERED AS A RESULT OF DEVELOPMENT WHEREBY TO PROVIDE A REVERSE IMAGE OF SAID DEVELOPED LATENT IMAGE IN TERMS OF THE HIGHLIGHTS OF SAID SUBJECT, SAID DEVELOPER BEING IN A QUANTITY SUFFICIENT TO DISSOLVE DEVELOP SAID LATENT IMAGE AND SAID LIQUID COMPOSITION BEING IN A QUANTITY SUFFICIENT TO DISSOLVE ALL OF SAID DEVELOPER AND TO REACT, IN PLACES WHERE SILVER DEVELOPMENT HAS OCCURRED, WITH SAID METALLIC SALT TO PROVIDE SAID REVERSE IMAGE, AND SAID PRODUCT INCLUDING AN OPAQUE, BLACK, WATER-PERMEABLE LAYER CARRIED BY SAID PHOTOSENSITIVE LAYER ON THE SIDE THEREOF ADAPTED TO BE POSITIONED IN FACING RELATION TO SAID BASE LAYER WHEN THE PHOTOSENSITIVE LAYER AND THE BASE LAYER ARE SUPERPOSED, AND WHEREIN SAID BASE LAYER IS TRANSPARENT AND SAID BLACK LAYER PROVIDES NONHALATION MEANS AND, IN ADDITION THERETO, A BLACK BACKGROUND AGAINST WHICH SAID REVERSE IMAGE FORMED OF WHITE PRECIPITATE IS READILY VIEWABLE. 